1. Technical Field
This invention relates generally to systems for sensing a low liquid level in a container, and more particularly to a new and improved system which minimizes false indications by more accurately monitoring the liquid level.
2. Background Information
There is a great demand for systems which can continuously monitor the level of liquid in a container and provide an immediate indication when the level falls below a desired minimum. Consequently, many such systems exist in the prior art for meeting that demand. In one such system, a probe is submerged into the liquid in a container, with its open lower end contacting the bottom of the container. The probe is coupled to a pressure switch through a fluid conduit. Air in the probe and the conduit is compressed by an amount which is a function of the static head of the liquid. Thus, when the level of the liquid drops, the fluid pressure in the probe drops correspondingly. When the fluid pressure in the probe drops below a predetermined level, the pressure switch is actuated to sound an alarm indicating a low liquid level.
A problem with the prior art system is that, over time, air is absorbed into the medium being monitored and the pressure switch or other system components tend to begin slowly leaking air, and this causes the pressure in the probe to drop. Consequently, when the pressure falls below the predetermined level the pressure switch is actuated and the alarm sounds, even though the liquid level in fact is not low. These false alarms are annoying to the operator of the equipment and cause numerous delays while the liquid level is manually checked. If the system for refilling the container is automated, an overfilling problem may result. Thus, a solution is needed to remedy these false alarms.